By breathing patterns we mean the aggregation of all oscillatory or pseudo-oscillatory variations appearing in the descriptors of individual breaths (i.e., inspiratory and expiratory duration and volumes, FRC, and ventilation). The characterization of a breathing pattern includes the strength and cycle time of the oscillatory component and the relationship between the breathing descriptors for each component. We are measuring and classifying breathing patterns in three types of subjects: healthy young adults at altitudes up to 14,000 ft., patients in a cardiac ICU and infants. The infants themselves fall into four categories: premature, normal term neonates, those deemed at risk for SIDS, normal age cohorts of the previous category. Breathing data on adults are taken by a magnetometer technique which preserves naivete. The objective is to provide a tool for the diagnosis of abnormal respiratory control function by relating breathing patterns to states of disease in patients or to risk of SIDS in infants.